In my opinion, this is better than the first GuP season, I liked how the author basically turned GuP universe into an edgy type of story, it took GuP into a whole new level tbh.
But the big drawbacks for me is the insertion of the big gay fanservice (Still, this is not a yuri manga tho) but the yuri foot fanservices are just unnecessary, this makes Rin into a joke of a character, she'll be always remembered as a girl who has foot fetish instead of anything remarkable unlike Shizuka which I will remember for her speeches and tactics.
And it's amazing that the author managed to insert this story into the parent story despite that it's started to publish before der Film, now it serves as a prequel to the das Finale anime and it ends RIGHT before Part 3 hit the theatres, we might probably see Shizuka and Rin as an easter egg at the 5th movie considering both characters now have seiyuus.
But yeah, solid 9/10. This won't become a full anime though sadly. Unless Actas sold the rights off to other company.